A display and input-output device providing or combining the touch screen (may be called as a touch panel), which is an input device, has been widely put in practical use as a display device such as a liquid-crystal display. In particular, a display and an input device are mainly used in a portable device such as cellular phone. A display and an input device with this touch screen are possible for users to operate devices intuitively by pushing on screen of display device.
Although there are various systems in the touch screen, a capacitive system is gradually increasing recently. The projected capacitive system having electrodes performed by a lot of patterning in x direction and y direction among the capacitive system is easy to detect multi-points touch and widespread rapidly recently.
On the other hand, in case of a surface-capacitive type regarding a planar electrode without patterning as a detection surface among the capacitive systems, there are a lot of needs for use required for robustness. Different points from the other systems will be the followings, (1) Sensitivity is obtained by not digital signal, but analogue signal, as there is no patterning on the electrodes. (2) There more sensitive even with a small capacitance (3) There are few influences caused by water sticking in order to measure an absolute capacitance between grounds (human body) and a planar electrode (4) The similar structure is applicable to various sizes ranging from a small type to a large type (5) A simple structure is applicable (6) Visibility is so good, as there are few laminated layers and there is no patterning in a visible part.
Next, the background art concerning the piezoelectric sheet will be described.
Piezoelectric effect (Piezoelectricity) is a phenomenon of electrical polarization (electrical charge on surface) generated at the time of affecting mechanical strain to a substance. The generated electric potential is proportional to a magnitude of strain and the polarity corresponds to a direction of strain. This phenomenon is reversible. When the same substance is electrically polarized by applying electric field to it, mechanical strain generates, or transforms the substance in proportion with a magnitude of the polarization.
There is a pyroelectric effect as a phenomenon similar to the piezoelectric effect. The pyroelectric effect (Pyroelectricity) is a phenomenon of electric polarization caused by the heat absorption in the substance. The generated electric charge is proportional to a magnitude of temperature change. All of the pyroelectric substance having Pyroelectricity shows the piezoelectricity.
On the other hand, some of piezoelectric substance having the piezoelectric effect does not have the pyroelectric effect.
As the material with the piezoelectricity, ceramics represented by PZT (lead zirconate titanate: Pb[ZrxTi1−x]O3) are greatly used. As there is a problem of toxicity including lead in piezoelectric ceramics, a large number of lead-free piezoelectric ceramics such as Bismuth ferrite (BiFeO3) has been developed. However, the ceramics has defects, in which it is not good at flexibility and machinability as its material is hard, and also it is hard to handle in a large area sheet.
On the other hand, the piezoelectric film using polymeric material has the following characteristics. It has flexibility (flexible and rich in elastic deformation), machinability (for example, easy to cut with scissors), shock resistance, high voltage resistance, water resistance, chemical stability, and the like, and also it is easy to make large area and thin film thereof. It has characteristics which are small in specific weight, light in weight, and a good transparency. Moreover, it has characteristics which have high voltage output, a wide range of frequency characteristics, low acoustic impedance, a large piezoelectric coefficient, and the like.
The polarized (poling) polyvinylidene fluoride (1, 1-2 ethane polymer fluoride, PVDF) of homopolymer represents a high piezoelectric property. Ceramics produces a piezoelectric effect by crystal structure of a material. On the other hand, PVDF is around 50% of semicrystalline polymer in crystallinity degree. As a long-chain molecules, which is mutually winding, are adhered to and detached in polymer, it shows behaviors which are different from piezoelectricity caused by a crystalline structure itself. Principally, PVDF is considered to generate the piezoelectric effect by two mechanisms. One is a piezoelectricity of a crystal caused by transforming dipole in the crystal by outside force, and the other is a piezoelectricity caused by scale effect, which shows a change of electric charges induced at electrodes by residual polarization, based on distortion of soft non-crystalline part.
The transparent piezoelectric sheet for detecting the pressure with use of polymer showing piezoelectricity described above is disclosed in Patent Literature 1.
Patent Literature 1 discloses a transparent piezoelectric sheet comprising a sheet-like transparent piezoelectric layer, a first transparent plate electrode disposed on one surface of the layer and a second transparent plate electrode disposed on the other surface of the layer. The transparent piezoelectric sheet is possible to detect the touch pressure and use as a transparent piezoelectric sheet for detecting the touch pressure. This transparent piezoelectric sheet for detecting the touch pressure gives a touch pressure detecting function on a touch panel for detecting the touch position by combining with the touch panel for detecting the touch position. This touch panel for detecting the touch position is designed to use a resistive-film touch panel which is low cost, or a projected capacitive touch panel which is easy to detect multi-points touch. With reference to FIG. 35 corresponding to FIG. 1 of Patent Literature 1, two transparent sheet members having the transparent plate electrodes 2122, 2123 on them are combined to face mutually the transparent plate electrodes 2122, 2123, and a sheet-like transparent piezoelectric layer 2121 is provided therebetween, under the touch panel 2210 of the resistive film or projected capacitive systems. The piezoelectric sheet 2120 is formed by the transparent plate electrodes 2122, 2123 and the sheet-like transparent piezoelectric layer 2121. The whole members are housed in the frame 2124. These configurations enable detections of both the touch position and the touch pressure.
On the other hand, Patent Literature 2 discloses a system detecting the touch position and the touch pressure by a touch panel for detecting the touch position of the projected capacitive system and the piezoelectric elements (pressure sensors) provided at four corners thereof.
Patent Literature 2 discloses a sensor device. FIG. 1 illustrating a Data Processing Unit with the sensor device of Patent Literature 2 will be referred as corresponding to FIG. 36. The sensor device is composed by a touch panel 2250, a housing 2210, and a pressure sensor 2260. The touch panel is applied as a capacitive system or a resistive film system. The touch panel of the capacitive system in Patent Literature 2 is, for example, configured to laminate a X electrode substrate and a Y electrode substrate to form a X transparent electrode pattern on the X electrode substrate and Y transparent electrode pattern on the Y electrode substrate, respectively. That is, the touch panel of capacitive system in Patent Literature 2 is the touch panel of projected capacitive system.
The pressure sensor 2260 has a first electrode fixed to the touch panel 2250, a second electrode fixed to a housing 2210, and an elastic body disposed between the touch panel and the housing. The pressure force pushed on an input operation surface is detected as a change of capacitance between the first electrode and the second electrode. This pressure sensor is disposed at four corners of the touch panel.
Moreover, the liquid-crystal panel 2230 is disposed at a rear surface of the touch panel 2250. The liquid-crystal panel 2230, the touch panel 2250, and the pressure sensor 2260 are stored in the housing 2210.